1. Field of the Invention
The present invention relates to a producing method of optical device, a positioning master, an optical device and a projector.
2. Description of Related Art
Conventionally, a projector including a plurality of optical modulators (liquid crystal panels) for modulating a plurality of colors lights in accordance with image information, a color-combining optical system (cross dichroic prism) for combining the color lights modulated by the respective optical modulators, and a projection optical system (projection lens) for enlarging and projecting the light combined by the prism to form a projection image has been used. So-called three-plate projector is known as such projector, where a light beam irradiated by a light source is separated into three color lights of red, green and blue by a dichroic mirror, which is modulated by three liquid crystal panels for each color light in accordance with image information, the modulated light beam is combined by a cross dichroic prism and the color image is enlarged and projected by a projection lens.
In order to obtain vivid projection image by such projector, focus and alignment adjustment of the respective liquid crystal panels has to be conducted with high accuracy in producing the projector for avoiding shift in picture element between the respective liquid crystal panels and distance shift from the projection lens. The above focus adjustment refers to an adjustment for accurately locating the respective liquid crystal panels at the back focus position of the projection lens and alignment adjustment refers to aligning the picture elements of the respective liquid crystal panels, which also apply in the following description.
The focus and alignment adjustment of the liquid crystal panel is conducted on an optical device having three liquid crystal panels and a cross dichroic prism, by (1) entering a light beam from an adjustment light source to be incident on image formation area of the respective liquid crystal panels (2) detecting the light beam incident on the light-incident surface of the cross dichroic prism and irradiated from the light-irradiating surface thereof by a light beam sensor; and (3) adjusting the relative position of the respective liquid crystal panels by a position adjustor while checking the focus and picture element position of the respective liquid crystal panels detected by the light beam sensor. Thus positioned respective liquid crystal panels are adhered and fixed using ultraviolet curing adhesive, thus producing a highly accurate optical device.
In order to produce an optical device according to the above steps, since the reference position (start position before adjustment) of the light beam sensor has to be obtained before conducting focus and alignment adjustment, a master optical device of which focus and alignment are highly accurately adjusted by other producing machine is prepared in advance and the reference position of the light beam sensor is set with reference to the position of the optical modulator of the master optical device.
Since the master optical device is for setting the reference position of the light beam sensor, the master optical device has to be highly accurately arranged considering optical characteristics of the projection lens. Accordingly, in a conventional arrangement, a machine dedicated for producing a master optical device having an optical device to be adjusted and a projection lens of average characteristics is prepared, while the master optical device is produced by highly accurately adjusting focus and alignment by introducing light beam into the optical device to be adjusted and sensing a projection image projected onto screen etc. through the projection lens with a CCD camera etc.
However, since a machine dedicated for producing the master optical device has to be prepared only for preparing a master optical device, production efficiency of optical device is deteriorated and the production cost of the optical device is increased.